The present invention relates to analog-to-digital converters and specifically to an extended precision in video-bandwidth analog-to-digital converter using optical techniques. The invention also relates to the particular configuration of such an analog-to-digital converter.
The function of an analog-to-digital converter (ADC) is to repetitively sample a time-varying waveform, usually at fixed time intervals, and generate a series of digital numbers to approximate the analog sample values.
Analog-to-digital converters (ADCs) are widely used to translate sensor measurements of an analog nature into the digital language of computing, information processing, and control systems. There is presently considerable interest in high-precision (8-10 bit) conversion at rates of 10-20 Msamples/sec for use in digital transmission and recording of television signals. However, for some applications (e.g., in radar signal processing), even higher precision at video sampling rates is desired for enhanced dynamic range. It has proven difficult to achieve precision beyond 10 bits at these rates using conventional silicon integrated circuit technology.
Previous optical ADC designs have made use of the periodic dependence of the transmission of an interferometric electro-optic modulator on applied voltage. Operation at rates greater than 100 Msamples/sec has been demonstrated in several laboratories, and recently 1 Gsample/sec performance was reported at Lincoln Laboratory. In those experiments, electronic comparators converted the optical signals from an array of N modulators into an N-bit binary word.